Effects of Small-Scale Dead Wood Additions on Beetles in Southeastern U.S
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Forests 2012, 3, 632-652; doi:10.3390/f3030632 OPEN ACCESS forests ISSN 1999-4907 www.mdpi.com/journal/forests Article Effects of Small-Scale Dead Wood Additions on Beetles in Southeastern U.S. Pine Forests Kier D. Klepzig 1,*, Michael L. Ferro 2, Michael D. Ulyshen 3, Matthew L. Gimmel 4, Jolie B. Mahfouz 5, Allan E. Tiarks 5 and Chris E. Carlton 2 1 USDA Forest Service, Southern Research Station, 200 WT Weaver Blvd, Asheville, NC 28804, USA 2 Department of Entomology, Louisiana State University, 404 Life Sciences Building, Baton Rouge, LA 70803-1710, USA; E-Mails: [email protected] (M.L.F.); [email protected] (C.E.C.) 3 USDA Forest Service, Southern Research Station, 201 Lincoln Green, Starkville, MS 39759, USA; E-Mail: [email protected] 4 Department of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA; E-Mail: [email protected] 5 USDA Forest Service, Southern Research Station, 2500 Shreveport Hwy, Pineville, LA 71360, USA; E-Mails: [email protected] (J.B.M.); [email protected] (A.E.T.) * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +1-828-257-4307; Fax: +1-828-257-4313. Received: 19 June 2012; in revised form: 14 July 2012 / Accepted: 25 July 2012 / Published: 15 August 2012 Abstract: Pitfall traps were used to sample beetles (Coleoptera) in plots with or without inputs of dead loblolly pine (Pinus taeda L.) wood at four locations (Louisiana, Mississippi, North Carolina and Texas) on the coastal plain of the southeastern United States. The plots were established in 1998 and sampling took place in 1998, 1999, and 2002 (only 1998 for North Carolina). Overall, beetles were more species rich, abundant and diverse in dead wood addition plots than in reference plots. While these differences were greatest in 1998 and lessened thereafter, they were not found to be significant in 1998 due largely to interactions between location and treatment. Specifically, the results from North Carolina were inconsistent with those from the other three locations. When these data were excluded from the analyses, the differences in overall beetle richness for 1998 became statistically significant. Beetle diversity was significantly higher in the dead wood plots in 1999 but by 2002 there were no differences between dead wood added and control plots. The positive influence of dead wood additions on the beetle community can be largely attributed to the saproxylic fauna (species dependent on dead wood), which, when analyzed separately, Forests 2012, 3 633 were significantly more species rich and diverse in dead wood plots in 1998 and 1999. Ground beetles (Carabidae) and other species, by contrast, were not significantly affected. These results suggest manipulations of dead wood in pine forests have variable effects on beetles according to life history characteristics. Keywords: arthropods; biodiversity; coarse woody debris; epigeic; insects; slash 1. Introduction Logs and other woody debris on the forest floor are an essential habitat for a wide range of saproxylic arthropods [1–3], which are directly or indirectly dependent on dead and dying wood [4]. These include not only phloem and wood feeders but also their predators and species associated with wood-decaying fungi. Many non-saproxylic ground-dwelling arthropods benefit from dead wood as well. For instance, a number of studies have shown litter-dwelling arthropods and other invertebrates to be more numerous immediately next to dead wood than short distances away from it [5–17]. These results can be attributed variously to dead wood providing a relatively stable source of moisture [18–20], shelter from predators or adverse weather conditions, and an abundance of prey or other food items. With demand for forest products continuing to rise (especially now with a growing interest in biofuel production, see [21,22]), understanding the role of dead wood in maintaining biodiversity, tree productivity and long-term forest sustainability is becoming more important in forest management. Of particular value are studies investigating the effects of dead wood manipulations on these interests. Several manipulative studies have demonstrated the positive relationship between dead wood and ground-dwelling arthropod diversity [23–25], but the question is far from resolved and has received little attention in many forest types. The forests of the southeastern United States are among the most productive in North America with loblolly pine (Pinus taeda L.) being the single most important timber species in the region. One of the few efforts to measure arthropod response to dead wood manipulations made in loblolly pine plantations began on the Savannah River Site in South Carolina in 1996. In the first phase of that study, plots in which all dead wood was removed annually were compared to reference plots from which no dead wood was removed. After pitfall-sampling ground-dwelling arthropods in those plots for five years, Hanula et al. [26] found no differences in overall abundance or morphospecies richness. Overall arthropod diversity and evenness were significantly lower in removal plots than in reference plots, however, and several families differed in abundance between the two treatments. These differences were observed only in the first two full years of sampling, however. In the second phase of the study, beginning in 2001, arthropods were sampled in these same plots for four more years. Two new treatments were added in which sampling also took place; one involving major inputs of logs to the forest floor and the other involving major inputs of dead standing trees. Contrary to expectations, but largely consistent with the first phase of the study, there were no differences in total ground-dwelling arthropod abundance, richness, diversity or composition among treatments [27]. Only ground beetles (family Carabidae) exhibited a significant association with dead wood. Forests 2012, 3 634 During 1998, a study was installed on four widely-separated USDA Long Term Soil Productivity (LTSP) sites in the Southeastern United States to better understand the importance of dead wood to nutrient cycling and biodiversity in pine forests. The responses of beetles, the most diverse arthropods on the forest floor, are reported here. 2. Materials and Methods This study took place at the following four LTSP sites: Croatan National Forest, Craven Country, NC, USA; DeSoto National Forest, Jones Country, MS, USA; Kisatchie National Forest, Rapides Parish, LA, USA; Davy Crockett National Forest, Trinity Country, TX, USA. The forests were dominated by 50–60 yr pine [loblolly in LA and NC, slash (P. elliottii Engelm.) in MS, and loblolly and shortleaf (P. echinata Mill.) in TX] with an understory consisting of oak (Quercus sp.), hickory (Carya sp.), and sweetgum (Liquidambar styraciflua L.). For this experiment, the coarse woody debris was added to remnant mature pine stand, adjacent to the LTSP treatment plots. At each site, three of the mature stand plots were used as controls and contained only the existing woody debris already present or that which fell during the study. A 30 × 45 m rectangular area at each site was divided into six 15 × 15 m plots. The dead wood added to all of the plots came from the same 43-year-old loblolly pine stand in the Palustris Experimental Forest, Louisiana. Sections of wood were removed from the main trunk (i.e., “logs”, 30–35 cm dbh, 1 m long), limbs (2.5–10 cm mid-length diam, 0.5 m long), and twigs (0.5–1.5 cm diam, 0.25 m long) of loblolly pine trees felled for this purpose. Ten logs, 8 limbs, and 24 twigs were distributed across the three randomly selected dead wood plots at each site in April and May 1998. At each given site, the material was added all at once, on one date during the time frame mentioned above. At all sites, the amount of existing coarse woody debris and the vegetation on the ground were roughly the same. Our additions of material impacted the sites in a very similar manner, adding the above material to the baseline of that already onsite. One pitfall trap (modified from [28]) was installed in each plot to sample ground-dwelling beetles. At each site, the trap was placed arbitrarily within the plot, in the immediate area of the added dead wood. Each trap consisted of a 15-cm-diameter plastic funnel fastened beneath a hole in the center of a 30 × 30 cm section of ~1.9 cm-thick plywood with bevelled edges. This assembly was positioned over a 2-liter plastic container, half-filled with a 1:1 mixture of propylene glycol and 95% ethanol, buried at ground level. Samples were collected approximately biweekly from May through September at all locations in 1998 and at all locations except for North Carolina in 1999. Additional samples were collected in all locations except for North Carolina in April and May of 2002. Specimens not identified below family level (117 individuals were only identified to family level) were excluded from the dataset. After pooling all sampling periods for a given year, analyses of variance (ANOVA) were carried out for each year separately (due to differences in sampling intensity) to determine whether beetle abundance (log(x + 1)-transformed to achieve normality), richness, or Shannon’s diversity varied between treatments. Site location (= “State”) was included in the model as a blocking variable and was treated as a random effect. To provide additional information, separate analyses were performed on the following three groups: saproxylic (species directly or indirectly dependent on dead or dying wood), non-saproxylic ground beetles, and other species. These Forests 2012, 3 635 designations were based on familiarity with the taxa and information available in the literature. Voucher specimens have been deposited in the Louisiana State Arthropod Museum, Baton Rouge, Louisiana.